Automotive internal combustion engine speed control is generally known to include both steady state and transient compensation strategies. The steady state strategy provides for engine speed reference tracking under engine steady state operating conditions with minimum steady state error. The transient strategy provides for disturbance rejection and transient compensation to substantially maintain the reference engine speed when engine load is changing or when disturbances are incident on the system.
Typically, the steady state compensation strategy processes input signals indicating the engine operating level and, through stored calibration values, generates a steady state engine output torque requirement. A control command is periodically adjusted to provide for the engine output torque requirement. Commonly, the control command is directed to an engine intake air rate control actuator, such as a bypass air valve, to vary engine intake air rate to achieve the output torque requirement. While not as responsive a torque control parameter as spark timing variation, the intake air rate control is sufficiently responsive to provide adequate torque control under most steady state engine operating conditions.
The accuracy of the intake air rate command for the steady state compensation strategy is limited by the accuracy of the stored calibration information. Generally, the steady state torque requirement Tss can be determined as follows EQU Tss=.function.(MAP,RPM,EST,A/F,AMB,TEMP,BARO)
in which MAP is engine intake manifold absolute pressure, RPM is engine speed, EST is spark timing advance, A/F is engine air/fuel ratio, AMB is ambient temperature, TEMP is engine coolant temperature, and BARO is barometric pressure. During a conventional calibration process, the parameters MAP, RPM, EST, and A/F can be varied without significant difficulty to provide a precise calibration of the resulting variation in Tss. However, the parameters AMB, TEMP and BARO are not easily controllably varied during a conventional calibration process and therefore are not accurately incorporated in the Tss calibration information, if at all. The result is an on-line compensation for engine speed error under both steady state and transient operating conditions caused by an inadequate calibration for changes in BARO, TEMP, and AMB. The on-line compensation typically includes controlling spark timing EST advance to compensate for such inadequate calibration. This reduces spark timing authority available to compensate for other transients and disturbances that may occur, which can reduce transient control performance. Further, any attempt at calibrating for change in TEMP, AMB, and BARO will be substantially inaccurate and will increase calibration time and difficulty, adding to automotive vehicle cost.
It would therefore be desirable to determine the effect of such slowly changing and difficult to calibrate parameters as BARO, AMB, and TEMP on the engine steady state torque requirement and to incorporate such learned information into the determination of the steady state torque requirement, to improve engine speed control reference tracking, to preserve ignition timing control authority, and to relieve a significant calibration burden.